Device and method for vector equalization of an OFDM signal

Abstract

The present invention belongs to the field of transmission of a signal, using OFDM modulation (Orthogonal Frequency Division Multiplexing), from a transmitter to at least one receiver, via a transmission channel. The invention relates in particular to a device and a method for equalization of the received OFDM signal. Said equalization device is fitted into the reception system between a synchronization module and a module for binary decoding of the received signal, in which the receiver includes a recursive vector equalizer (10) capable of correcting the received signal in the time domain. According to the invention, the recursive vector equalizer (10) includes computation means (16; 22; 24; 40; 44; 46; 56) capable of estimating each transmitted symbol as a function of an estimate of the transmitted symbol which precedes the said transmitted symbol.

What is claimed is: 
     
       1. Device for transmitting an OFDM signal formed by a plurality of digital symbols transmitted from a transmitter to at least one receiver, via a transmission channel, in which the receiver includes a recursive vector equalizer capable of correcting the received signal in the time domain, wherein the recursive vector equalizer includes computation means capable of estimating each transmitted symbol as a function of an estimate of the transmitted symbol which precedes said transmitted symbol. 
     
     
       2. Device according to claim 1, wherein the receiver includes at least two estimators capable of dynamically computing the coefficients of at least two triangular matrices representing the impulse response of the transmission channel. 
     
     
       3. Device for transmitting an OFDM signal formed by a plurality of digital symbols transmitted from a transmitter to at least one receiver, via a transmission channel, in which the receiver includes a recursive vector equalizer capable of correcting the received signal in the time domain, wherein the recursive vector equalizer includes computation means capable of estimating each transmitted symbol as a function of an estimate of the transmitted symbol which precedes said transmitted symbol; wherein the receiver includes at least two estimators capable of dynamically computing the coefficients of at least two triangular matrices representing the impulse response of the transmission channel; and wherein   said estimator includes means for computing the coefficients of the inverse matrix of a first lower triangular matrix Ho and the coefficients of a second upper triangular matrix H 1 .   
     
     
       4. Device for transmitting an OFDM signal formed by a plurality of digital symbols transmitted from a transmitter to at least one receiver, via a transmission channel, in which the receiver includes a recursive vector equalizer capable of correcting the received signal in the time domain, wherein the recursive vector equalizer includes computation means for estimating each transmitted symbol as a function of an estimate of the transmitted symbol which precedes said transmitted symbol; wherein the computation means of the equalizer consists on the one hand, of a subtractor having a first input to which the received signal is applied, this subtractor is connected in a forward branch, in series with a first multiplier and with a module for discrete Fourier transform computation, a first input of this first multiplier is connected to the output of the subtractor and a second input of this first multiplier is connected to the output of the first estimator of the inverse of the matrix H 0 , whereas the output of this first multiplier is connected to the input of the module for discrete Fourier transform computation, an output of which delivers a vector representing a first estimate of the transmitted symbol, and, on the other hand, of a hard decision module, arranged in a feedback loop, in series with a module for inverse discrete Fourier transform computation and with a second multiplier, the input of said hard decision module is connected to the output of the module for Fourier transform computation, whereas the output of said hard decision module is connected to the input of the module for inverse discrete Fourier transform computation, the output of which is connected via a storage module, capable of storing at least one symbol, to a first input of the second multiplier, a second input of this second multiplier is connected to the output of the estimator of the matrix H 1 , the output of the second multiplier is connected to a second input of the subtractor and delivers thereto a vector obtained by computing the inverse Fourier transform of the estimated value of the symbol transmitted before, followed by multiplication of this transform by the matrix H 1 .   
     
     
       5. Method for equalization of an OFDM signal carrying a plurality of digital symbols, each including a number N of complex samples obtained by constellation coding of the signal to be transmitted, each symbol being represented by a vector of N components, this signal is transmitted by a transmitter to at least one receiver, via a transmission channel whose impulse response, previously estimated and stored, is represented by at least two matrices, namely a first lower triangular matrix H 0  and a second upper triangular matrix H 1 , said method comprising the steps of subtracting, from the vector representing the received symbol, the vector obtained by computation of the inverse discrete Fourier transform followed by multiplication of the matrix H 1  of an estimated value of the preceding symbol,   multiplying the vector resulting from the subtracting step by the inverse of the matrix H 0 , then   computing the Fourier transform of the vector resulting from the multiplying step so as to express the corrected symbol in the original frequency domain,   using the symbol obtained by this Fourier transform from the computing step to correct the following received symbol,   computing a new estimate of the coefficients of the inverse matrix of H 0  and the coefficients of the matrix H 1 , and   storing the estimated values to correct the following symbol.   
     
     
       6. Method according to claim 5, wherein in order to estimate the coefficients of the inverse matrix of H 0  and the coefficients of the matrix H 1 , only the coefficients of the first column of the said inverse matrix of H 0 , and the coefficients of the first row of the said matrix H 1 , are computed.